Synthesis and spectral characterization of acetophenone thiosemicarbazone-A nonlinear optical material

Article abstract of DOI:10.1016/j.saa.2010.03.030

Acetophenone thiosemicarbazone (APTSC) was synthesized. Solubility of APTSC was determined in ethanol and methanol at different temperatures. Single crystals were grown from ethanol by slow evaporation at room temperature. The grown crystal was subjected

Full text of DOI:10.1016/j.saa.2010.03.030

Spectrochimica Acta Part A 76 (2010) 369–375
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and spectral characterization of acetophenone thiosemicarbazone—A
nonlinear optical material
R. Santhakumaria, K. Ramamurthib,∗, G. Vasukic, Bohari M. Yamind, G. Bhagavannarayanae
a Department of Physics, Govt. Arts College for Women, Pudukkottai 622 001, Tamil Nadu, India
b Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India
c Department of Physics, K.N. College of Arts and Science, Thanjavur 613 007, Tamil Nadu, India
d School of Chemical Sciences and Food Technology, Kebangsaan Universiti, Bangi, Selangor 43650, Malaysia
e Materials Characterization Division, National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110 012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Acetophenone thiosemicarbazone (APTSC) was synthesized. Solubility of APTSC was determined in
ethanol and methanol at different temperatures. Single crystals were grown from ethanol by slow evapo-
ration at room temperature. The grown crystal was subjected to FTIR, Laser-Raman and 1H NMR spectral
analyses to confirm the synthesized compound. Thermal properties were investigated by thermogravi-
metric and differential thermal analyses. High-resolution X-ray diffractometry (HRXRD) was employed
to evaluate the perfection of the grown crystal. The range and percentage of optical transmission was
ascertained by recording UV–vis–NIR spectrum. The third order nonlinear optical parameters (nonlinear
refractive index and nonlinear absorption coefficient) were derived by the Z-scan technique.
© 2010 Elsevier B.V. All rights reserved.
Received 28 December 2009
Received in revised form 12 March 2010
Accepted 17 March 2010
PACS:
81.10.Dn
61.66.Hq
65.60.+a
42.65.Ky
Keywords:
Organic compounds
Solution growth
Powder diffraction
Nuclear magnetic resonance
Nonlinear optical materials
1. Introduction
gated structure [6,7]. Recently there has been considerable interest
in the co-ordination chemistry of thiosemicarbazones because of
Progress in the area of nonlinear optics depends upon the devel-
opment of new materials. When compared with the inorganic
materials, organic and semiorganic materials are attracting a great
deal of attention, as they have large optical susceptibilities, inherent
ultra fast response time and good optical properties [1–4]. Organic
compounds are often formed by weak van der Waal’s and hydro-
gen bonds and possess high degree of delocalization. Hence they are
optically more nonlinear than inorganic materials. Apart from their
merits of flexibility in the methods of synthesis and inherently high
nonlinearity, crystalline organic nonlinear optical (NLO) materials
are difficult to grow in large size with good optical quality and the
fragile nature of these crystals often makes them difficult to process
[5]. The poor laser damage threshold limits these crystals in many
optical applications. Organic molecules with remarkable nonlinear
activity mostly consist of ␲-electron conjugation with an electron
donor group and an acceptor group at the extreme ends of a conju-
their biological activities and their nonlinear optical properties [8].
It has been postulated that extensive electron delocalization in
the thiosemicarbazone moiety helps the free thiosemicarbazone
ligands and their metal complexes to improve second harmonic
generation (SHG) efficiency [9–11]. Thiosemicarbazide has been
shown to be a good ligand for a range of metals, including zinc,
mercury, cadmium and nickel [12,13]. Earlier works suggest that
these complexes offer an excellent opportunity for the study of the
effects of ligand system on the formation of nanomaterials and also
the importance of the compounds containing thiosemicarbazide
moiety in medicinal uses [14]. Single crystal of acetophenone
thiosemicarbazone is one of the potential organic nonlinear opti-
cal materials, which belongs to the ketone group of compounds.
The sub-group of ketone is asymmetrical (chiral carbon). Hence in
the present investigation we report on the synthesis and growth of
acetophenone thiosemicarbazone (APTSC) crystal by slow evapo-
ration at room temperature and the characterization of the grown
crystal by single crystal XRD, HRXRD, FTIR, Laser-Raman, 1H NMR,
UV–vis–NIR, Vickers microhardness and thermal analyses and on
the third order nonlinear optical properties.
∗
Corresponding author. Tel.: +91 431 2407057.
E-mail address: krmurthin@yahoo.co.in (K. Ramamurthi).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.03.030

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R. Santhakumari et al. / Spectrochimica Acta Part A 76 (2010) 369–375
Scheme 1.
show C H deformation vibration in the region 710–690 cm−1 [15],
2. Experimental
the presence of C H deformation is evident from the vibration at
685 cm−1. The peak observed at 841 cm−1 is due to the out-of-
plane aromatic C H bond. The C S stretch of the thiosemicarbazide
moiety is observed at 1093 cm−1. Absence of characteristic ketone
band between 1725 cm−1 and 1705 cm−1 (C O stretching) indi-
cates that there is no ketone group in the final product [17].
The Laser-Raman spectrum was recorded using Raman System, R-
3000, solid state laser (532 nm with green light) in the range of
2.1. Synthesis and growth of APTSC single crystals
APTSC was synthesized by reacting analytical grade acetophe-
none and thiosemicarbazide in 1:1 molar ratio in the distilled water.
The prepared solution was stirred well using magnetic stirrer and
if the solution appeared to be turbid methanol/ethanol was added
further and gently warmed until a clear solution was obtained.
The APTSC compound was synthesized according to the chemical
reaction depicted in Scheme 1.
Studies on the solubility at various temperatures showed
that APTSC has relatively high solubility in ethanol compared
to methanol (Fig. 1). Hence ethanol was chosen as the sol-
vent in the present work. Transparent APTSC crystals of about
0.5 mm × 0.5 mm × 0.5 mm were obtained from ethanol by slow
evaporation at room temperature and one of the optically good
quality crystals was used as seed crystal. Slow evaporation at room
temperature yielded a good quality single crystal of dimensions
8 mm × 7 mm × 2 mm in a growth period of 15 days and is shown
in Fig. 2.
100–3600 cm−1. In Laser-Raman spectrum C H stretching, C
H
deformation (in plane), C H deformation (out-of-plane) vibra-
tions are observed at 2795 cm−1, 113 cm−1, 857 cm−1 respectively.
The C N, C C, stretching vibrations are observed at 1606 cm−1
,
1504 cm−1 respectively. NH2 rocking is observed at 1113 cm−1. The
Laser-Raman spectrum presented in Fig. 4 also shows the presence
3. Characterization
3.1. FTIR and Laser-Raman spectral analyses
FTIR and Laser-Raman spectral analyses were carried out to
characterize the functional groups of the APTSC crystal molecules
[15,16]. FTIR spectrum was recorded for the purified sample
using P−e1rkin Elmer Paragon-500 by KBr pellet technique between
400 cm and 4000 cm−1 and is shown in Fig. 3. The band obtained
at 1589 cm−1 is due to the formation of imine group (C N) between
ketone and amine [17]. A weak absorption, observed at 2958 cm−1
is due to C H stretching. The peak at 3402 cm−1 is due to NH2
asymmetric stretching and an absorption peak at about 3140 cm−1
is due to NH stretching. The band appeared at 1497 cm−1 con-
firms the C C stretching frequency. As mono substituted benzenes
Fig. 2. The as-grown APTSC crystal.
Fig. 1. Solubility curve of APTSC.
Fig. 3. FTIR spectrum of APTSC crystal.

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371
Table 1
Important spectral band assignment of FTIR and Laser-Raman lines of APTSC.
Experimental wave number (cm−1
)
Modes of vibration
FTIR
Laser-Raman
2958(m)
1589(s)
1497(s)
1315
2795(m)
1606(s)
1504(m)
1315
1113
1010
–
␯(C H)
␯(C N)
␯(C C)
␯(C NH2)
␳(NH2)
␦(C H) in plane
␯(C S)
␦(C H) out-of-plane
␦(C H)
1115
1110
1093(m)
841
857
759(s)
777(s)
(s)Strong; (m)medium.
(␯) Stretching; (␦) bending or deformation; (␳) rocking.
peak observed at ı = 2.31 ppm is corresponding to methyl group
(CH3). The aromatic proton ortho to imine bond is observed at
ı = 7.71 ppm as a multiplet, whereas the remaining aromatic pro-
tons resonated at ı = 7.41 ppm as a multiplet. Similarly the NH2
protons of hydrazide part is observed at ı = 8.91 ppm as a broad
singlet, whereas the NH proton is observed at ı = 6.92 ppm [15].
Thus the formation of hydrazone is confirmed by NMR spectral
analysis.
Fig. 4. Laser-Raman spectrum of APTSC crystal.
of the functional groups of APTSC crystal. The observed vibra-
tional frequencies of FTIR and Laser-Raman spectra are tabulated
in Table 1.
3.3. Single crystal and powder XRD
The intensity data were collected at 298 K on a ‘SADABS (Bruker,
2000)’ system using MoK␣ graphite monochromated radiation.
The molecular structure of the crystal APTSC (C9H13N3SO) was
refined by the least squares method using anisotrophic ther-
mal parameters: R = 5.1%. The compound APTSC crystallizes in
orthorhombic system of Pbca. The parameter values calculated are
a = 15.429(3) Å, b = 7.127(7) Å, c = 8.340(7) Å, and Z = 8. The molecule
3.2. NMR spectral analysis
The proton NMR (1H) spectral analysis was carried out on the
APTSC crystal in CDCl3 using Bruker AC200-NMR Spectrometer
and is shown in Fig. 5. In the proton NMR spectrum of APTSC, a
Fig. 5. NMR spectrum of APTSC crystal.

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R. Santhakumari et al. / Spectrochimica Acta Part A 76 (2010) 369–375
Fig. 8. Morphology of the APTSC crystal.
3.4. High-resolution X-ray diffraction analysis
The crystalline perfection of the grown single crystal was char-
acterized by high-resolution X-ray diffraction (HRXRD) analysis by
employing a multicrystal X-ray diffractometer [18]. The well colli-
mated and monochromated MoK␣1 beam obtained from the three
monochromator Si crystals set in dispersive (+, −, −, +) configura-
tion was used as the exploring X-ray beam. The specimen crystal
was aligned in the (+, −, −, +) configuration. Due to dispersive
configuration, though the lattice constant of the monochromator
crystal(s) and the specimen are different, the unwanted dispersion
broadening in the diffraction curve (DC) of the specimen crystal is
insignificant. The specimen can be rotated about the vertical axis,
which is perpendicular to the plane of diffraction, with minimum
angular interval of 0.4ꢀꢀ. The DC was recorded by the so-called ω
scan wherein the detector was kept at the same angular position
2ꢁB with wide opening for its slit.
Before recording the diffraction curve the non-crystallized
solute atoms remained on the surface of the crystal and also to
ensure the surface planarity, the specimen was first lapped and
chemically etched in a non-preferential etchent of water and ace-
tone mixture in 1:2 volume ratio. Fig. 9 shows the high-resolution
diffraction curve (DC) recorded for a typical APTSC single crys-
tal specimen using (3 1 2) diffracting plane in symmetrical Bragg
geometry by employing the multicrystal X-ray diffractometer. The
Fig. 6. The molecular structure of APTSC crystal.
is nearly planer. The structure is stabilized by N H· · ·S intermolecu-
lar hydrogen bonds. The molecular structure of the title compound,
together with the atom labeling scheme and the intramolecular
hydrogen bonding, is shown in Fig. 6. The thiocarbonyl S atom
acts as a single acceptor for both hydrogen bonds. The arrange-
ment of the non-hydrogen atoms is nearly planar with the S and
the hydrazinic NH2 group is in a transposition with respect to
the C NH. The powder X-ray diffraction was recorded using pow-
der X-ray diffractometer with CuK␣ radiation (ꢀ = 1.5406 Å). Finely
crushed powder of APTSC crystal was scanned in the 2ꢁ values
ranging from 10◦ to 80◦. The obtained peaks were indexed and
are shown in Fig. 7. The morphology of the grown APTSC crystal
is shown in Fig. 8.
Fig. 7. Powder XRD pattern of APTSC.
Fig. 9. HRXRD spectrum of APTSC crystal.

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373
Fig. 10. UV–vis–NIR spectrum of APTSC.
Fig. 12. Z-scan (close and open) spectrum of APTSC.
solid line (convoluted curve) is well fitted with the experimental
points represented by the filled rectangles. On deconvolution of the
diffraction curve, it is clear that the curve contains an additional
peak, which is 134ꢀꢀ away from the main peak. This additional peak
depicts an internal structural low angle (tilt angle > 1ꢀ but less than a
deg.) boundary [19] whose tilt angle (misorientation angle between
the two crystalline regions on both sides of the structural grain
boundary) is 134ꢀꢀ from its adjoining region. The FWHM (full width
at half maximum) of the main peak and the low angle boundary are
respectively 102ꢀꢀ and 234ꢀꢀ. Though the specimen contains a low
angle boundary, the relatively low angular spread of around 600ꢀꢀ of
the diffraction curve and the low FWHM values show that the crys-
talline perfection is fairly good. Thermal fluctuations or mechanical
disturbances during the growth process could be responsible for the
observed low angle boundary. It may be mentioned here that such
low angle boundaries could be detected with well resolved peaks
in the diffraction curve only because of the high-resolution of the
multicrystal X-ray diffractometer used in the present study.
measuring the sign and magnitude of nonlinear refractive index
(n2) that has the sensitivity compared to interferometric meth-
ods. Using a single Gaussian laser beam in tight focus geometry,
as depicted in Fig. 11, the transmittance of a nonlinear medium
through a finite aperture in the far field as a function of the sample
position Z can be measured with respect to the focal plane. The non-
linear absorption and refractive index of APTSC crystals (thickness
∼1.7 mm) were estimated using the single beam Z-scan method
with CW laser beam intensity of 35 mW and the wavelength of
632 nm. The study of nonlinear refraction by the Z-scan method
depends on the position (Z) of the thin samples under the investi-
gation along a focused Gaussian laser beam. The sample causes an
additional focusing or defocusing, depending on whether nonlinear
refraction is positive or negative. In the most reported experiments,
0.1 < S (transmittance) < 0.5 has been used for determining nonlin-
ear refraction. Obviously, the linear transmittance of the aperture
S = 1 corresponds to the collection of all transmitted light and there-
fore is insensitive to any nonlinear beam distortion due to nonlinear
refraction [24]. Such a scheme, referred to as an “Open aperture”
Z-scan, is suited for measuring nonlinear absorption in the sample.
Results obtained from a typical closed aperture Z-scan study for
the grown APTSC are presented in Fig. 12. The nonlinear refractive
index (n2) of the crystal was calculated using the standard relations
given below [22–24].
3.5. Linear and nonlinear optical properties
In order to estimate the optical transparency in the
200–1100 nm region of the electromagnetic spectrum, the
optical transmittance study is carried out on the APTSC crystal
of thickness ∼2 mm employing Varian Cary 5E UV–vis–NIR spec-
trophotometer (Fig. 10). The lower cut off wavelength of the APTSC
is about 300 nm and the transmittance of the crystal is about 90%
in the entire visible and near infrared region which is an essential
parameter required for frequency doubling process [20].
0.406 (1 − S)0.25∗
ꢂTP–V
=
(1)
ꢂϕo
where ꢂTP–V is the difference between the normalized peak and
valley transmittance. ꢂTP–V/ꢂϕo is the on-axis phase shift at the
focus. The nonlinear refractive index (n2) and nonlinear absorption
coefficient (ˇ) are given by
3.6. Z-scan technique
In present case, we choose to work at 632 nm in order to eval-
uate materials at visible wavelengths in which there exist interest
for switchable holographic filters and refractive optical limiters
[21]. Hence the Z-scan method has gained rapid acceptance by
the nonlinear optics community as a standard technique for sep-
arately determining the nonlinear changes in refractive index and
change in optical absorption. Sheik-Bahae et al. [22] and Vanstry-
land and Sheik-Bahea [23] have reported a single beam method for
ꢂϕo
n2
=
(2)
kIoLeff
where ꢂϕo = 4.752, k = 0.118 × 109, Io = 6.85 × 103 kW/cm2,
Leff = 0.1150 × 10−3 m and
√
2
2ꢂT
ˇ =
(3)
I0Leff
Fig. 11. Experimental setup for the Z-scan measurements.

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R. Santhakumari et al. / Spectrochimica Acta Part A 76 (2010) 369–375
Fig. 13. Excitation spectrum of APTSC.
Fig. 14. Emission spectrum of APTSC.
where ꢂT = 0.04957,
k is the wavenumber (k = 2ꢃ/ꢀ) and
APTSC was studied by thermogravimetric analysis (TGA) and dif-
ferential thermal analysis (DTA) using SDT Q600 V8.3 Build 101
instrument between the temperatures 50 ◦C and 1100 ◦C at a heat-
ing rate of 10 ◦C/min under Nitrogen atmosphere (Fig. 15). The
APTSC monohydrate sample weighing 3.6400 mg is taken for the
measurement. There are three weight losses noted in the ther-
mogram. The earlier one is due to expulsion of solvent molecules
present in the crystals. The second and third major weight losses
are observed just above 220 ◦C and 450 ◦C. It is due to decomposi-
tion of APTSC crystal. From the DTA curve it is observed that, the
material is stable up to 165 ◦C, the melting point of the substance.
Above this point, the material begins to attain an endothermic tran-
sition and begins to decompose. The sharpness of this endothermic
peak shows the good degree of crystallinity of the sample [27]. The
graph also revealed that the material is fully decomposed at 535 ◦C.
Leff = [1 − exp(−˛L)]/˛ with Io = P/(ꢃωo2) defined as the peak inten-
sity within the sample, where L is the thickness of the sample, and
˛ is the linear absorption coefficient. The ratio of the signals with
and without the aperture accounts for the nonlinear absorption
and gives the information about purely nonlinear refraction. The
enhanced transmission near the focus is indicative of the saturation
of absorption at high intensity. Absorption saturation in the sample
enhances the peak and decreases the valley in the closed aperture
Z-scan. The focusing effect is attributed to a thermal nonlinearity
resulting from absorption of radiation at 632 nm. Localized absorp-
tion of a tightly focused beam propagating through an absorbing
medium produces a spatial distribution of temperature in the crys-
tal and consequently, a spatial variation of the refractive index that
acts as a thermal lens resulting in phase distortion of the propagat-
ing beam (Fig. 12). The nonlinear absorption property of the D–ꢃ–A
type ␲-electron system can be related closely to the ␲-electron
conjugate degree and delocalization capacity of the molecule. The
three dimensional X-ray crystal structure solution of this crystal
showed that the tortion angles C1–C6–C7–N1 and C5–C6–C7–N1,
in these conjugated chains are coplanar (Fig. 6.). These are all
favourable to nonlinear optical absorption, especially to saturated
absorption. Nonlinear refractive index (n2) of the APTSC calculated
is 5.11 × 10−8 cm2/W for the laser wavelength at 632 nm and the
value of nonlinear absorption coefficient (ˇ) (Fig. 12) estimated
from the open Z-scan curve is 0.1763 cm/W.
3.9. Microhardness analysis
Vickers microhardness test was carried out on APTSC crystal
using microhardness tester fitted with a diamond indenter. The
indentations were made using a Vickers pyramidal indenter for
various loads from 50 to 100 g in steps of 25 g. The diagonals of
the impressions were measured using Shimadzu (Japan); Model
HMV-2 hardness instrument. The measurements were made on the
well-developed (0 1 1) face. The indentation time was kept as 25 s
for all the loads. Vickers microhardness number (Hv) was evaluated
3.7. Fluorescence studies
Fluorescence may be expected generally in molecules that are
aromatic or contain multiple conjugated double bonds with a high
degree of resonance stability [25]. Fluorescence finds wide applica-
tion in the branches of biochemical, medical and chemical research
fields for analyzing organic compounds. The excitation and emis-
sion spectra for APTSC were recorded using Varian Carry Eclipse,
Fluorescence Spectrometer. The excitation spectrum was recorded
in the range 200–400 nm (Fig. 13). The sample was excited at
239 nm. The emission spectrum (Fig. 14) was measured in the range
300–600 nm and the emission peak was observed about 388 nm.
Thus the results indicate that APTSC crystal has the blue fluores-
cence emission.
3.8. Thermal analysis
Thermogram provides information about decomposition pat-
terns of materials and weight loss [26]. The thermal stability of
Fig. 15. TGA/DTA curve of APTSC crystal.

R. Santhakumari et al. / Spectrochimica Acta Part A 76 (2010) 369–375
375
the DTA curve corresponds to the melting point of the material.
Optical transmittance window and the lower cut off wavelength
identified through UV–vis–NIR and fluorescence spectrum revealed
that APTSC is a potential candidate for optical devices. The micro-
hardness study revealed that the crystal develops cracks for load
above 50 g. High-resolution X-ray diffraction study showed that
the perfection of the crystal is fair even though it contains a low
angle boundary. The relative third order nonlinear optical absorp-
tion and the nonlinear optical refractive index were calculated by
the Z-scan technique and reveals the suitability of the materials to
be utilized in generating third order harmonics.
Acknowledgements
One of the authors (RS) thanks Dr. K. Panchanatheeswaran, Pro-
fessor in Chemistry (Rtd), Bharathidasan University, Tiruchirappalli
for fruitful discussion and University Grant Commission, Govern-
ment of India for financial assistance [File No. MRP 2976/2009
(RS)]. Authors thank Dr. K. Sivakumar, Anna University, Chennai,
for extending lab facilities to record the Laser-Raman spectrum and
Dr. D. Sasti Kumar, Department of Physics, NIT, Tiruchirappalli, for
the support in recording the Z-scan measurements. The authors
thank CECRI, Karaikudi, for extending the lab facilities to record
the fluorescence spectrum.
Fig. 16. Microhardness values vs load for APTSC crystal on (0 1 1).
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4. Conclusion
Acetophenone thiosemicarbazone was synthesized using ace-
tophenone and thiosemicarbazide in the aqueous solution.
Solubility test revealed that ethanol is a suitable solvent for growing
single crystals of APTSC compared to methanol. The single crystal of
dimensions 8 mm × 7 mm × 2 mm was grown by the slow evapora-
tion technique at room temp. Determination of unit cell parameters
by the single crystal X-ray diffraction technique confirmed the
identity of the synthesized material. From the FTIR, Laser-Raman
and 1H NMR spectrum, the formation of the imine group of the
material was confirmed. Thermal analyses indicated that the crys-
tal has good thermal stability. A sharp peak observed at 165 ◦C in